The proposed postdoctoral NRSA incorporates a comprehensive research and training plan for the study of cilia function in the regulation of olfactory horizontal basal cells (HBCs) in the developing, mature, or injured olfactory epithelium (OE). The OE is comprised of various cell types including olfactory sensory neurons (OSNs), which are responsible for detecting odorants. When OSNs undergo cell death, they are readily replaced by a population of stem/progenitor cells found in the basal region of the OE. These stem/progenitor cells include globose basal cells (GBCs), which are an active cell population, and HBCs, which are quiescent. Although the OE has the capacity for self-renewal and constitutive neurogenesis, olfactory dysfunction can arise from various causes including age and environmental insults. What remain unknown are the precise mechanisms that regulate the stem cell properties of olfactory basal stem cells, including the signals that trigger a quiescent stem cell to become active. It is well known that OSNs possess cilia and new data from our laboratory show, for the first time, that HBCs also possess primary cilia. Because cilia are important for detecting external signals that regulate cellular function, our novel finding of cili on HBCs establishes a new potential role for cilia in the OE. We hypothesize that cilia are necessary for the regulation of HBC proliferation and differentiation. Aim 1 of this proposal will use mouse models, in which cilia maintenance and function are altered, to investigate the role of cilia in HBC proliferation and differentiation in developing and mature OE. This investigation will utilize an inducible conditional knockout mouse, in which cilia are specifically depleted from HBCs, and two mouse models of a ciliopathy, the growing class of cilia disorders linked to olfactory dysfunction. Aim 2 of this proposal will use the same conditional knockout mouse from Aim 1, to study the role of cilia on HBCs during the restoration of the OE. Surgical ablation of the olfactory bulb (bulbectomy) and chemical/pharmacological lesion will be utilized to induce cell type specific injury in the OE. The cell composition of the OE will be analyzed in order to investigate the ability of HBCs, without cilia, to restore the OE upon an injury. Finally, adenovirl infection will be used to determine whether HBCs are able to repopulate the OE after genetic rescue of cilia. The results from these studies will provide new insight into the regenerative properties of the OE and may also reveal new mechanisms for the etiology of olfactory dysfunction.